This invention relates to electronic timepieces, herein intended to mean timepieces of the type having an electronic oscillator, such as a quartz crystal oscillator, serving as a stable source of regular electrical pulses which constitute the time standard for the timepiece. To receive reasonable consumer acceptance, a modern electronic wristwatch or other body-worn timepiece must have certain basic features and capabilities, including the following (not necessarily in the order discussed). It must be accurate--errors of less than about 10 seconds per month are expected. Secondly, the power requirements must be sufficiently low so that frequent replacement of the battery or batteries is not required. Thirdly, in the case of wristwatches, the timepiece must be compact, particularly in the thickness dimension, in order that the watch does not interfere with clothing and is not otherwise burdensome to wear. Fourthly, the timepiece must be convenient in its operation and have a highly visible time display--preferably a display which is highly visible under low as well as high level ambient lighting conditions. Fifthly, the cost of acquiring and maintaining the timepiece must be reasonable.
This invention is applicable to horological instruments in general, however, it is believed to be most advantageously adapted for exploitation in a wristwatch; accordingly, the ensuing discussion will be based on wristwatch implementations of the invention. This invention is directed to providing an improved electronic watch, i.e., a watch having an electronic oscillator as a time standard and having either an electro-mechanical or an electro-optical time display. One type of commercially available electronic watch utilizes an electro-mechanical time display comprising a pulse-driven stepping motor coupled through a transmission (typically a gear train) to a set of hour, minute and second hands. The stepping motor may also drive ancillary time display devices such as day and/or date dials. Typically, the stepping motor input is a stable train of electrical pulses supplied from a logic circuit at a 1 Hz rate. The pulses cause the stepping motor rotor to incrementally advance one step per second. The rotor drives the watch second, minute and hour hands through an intermediate gear train.
A second general type of electronic watch is sometimes termed the "all electronic" or "all solid state" type which does not effect conversion of electrical energy to mechanical energy to display time functions, but rather employs an electro-optical time display. "Electro-optical" displays are herein intended to mean solid state or liquid state displays in which an optical pattern is created by the application of a pattern of voltages.
In such electro-optical displays the light-emitting or light-affecting (light-reflecting or light-absorbing) elements are arranged in segments, typically seven segments per digit displayed. The individual segments are selectively energized in patterns according to patterns of applied voltages to determine the digit displayed. There is typically provided between a quartz crystal oscillator and the electro-optical display a system of frequency dividers, counters and other appropriate logic circuitry and switches for appropriately determining the output reading of the electro-optical displays.
Each of the above-described types of electronic watches, i.e., those with electro-mechanical displays and those with electro-optical displays, are plagued by their own set of problems and limitations. The electronic watches which employ electro-mechanical displays are considered to be undesirably bulky and to consume an undersirably large amount of electric power. Such watches are non-innovative in the visual appearance of their time displays (typically conventional second, minute and hour hands with or without day or date dials), and thus hide from the consumer the innovative characteristics of the drive system for such watches. They also suffer from the long-recognized shortcoming of being difficult to read under low ambient lighting conditions.
Conventional electronic watches which have stepping-motor-driven displays and conventional date or day/date read-outs typically suffer also from a motor torque overloading at midnight. That is, at midnight, energy which has been stored in a spring by the stepping motor during the day is triggered to advance the day/date dial(s). The requirement that the stepping motor load the dial(s) advance spring is severe and can be as great as 4-5 times the normal motor loading.
The other type of electronic watch, namely the type having an electro-optical display for presenting time functions, also have drawbacks which have, to date, limited the market for such watches. The watches which employ LED (light-emitting diode) displays suffer from having undesirably large power requirements which necessitate that the time display be operated only on command. This is considered by many consumers to be a great inconvenience since he has not been accustomed to be thus inconvenienced to learn the time of day. Secondly, watches of the type having LED displays are more bulky than the consumer would like. They have, however, enjoyed prestige as a result of the novel, eye-catching light-emissive character of their displays. Electronic watches having LED displays are readable at night and thus have a significant advantage in this respect over non-self-illuminated time display devices.
Thirdly, in contrast with watches having a conventional mechanical display, the user of a watch with an electro-optical display is deprived of the advantage of computing the time interval between the present time and a future point in time by using the minute hand and the dial of his watch. Subconsciously nearly every watch user tends to do this. For example, if one has an appointment at 2:45 and one's watch indicates 2:25, the user simply determines the number of minutes left by counting on his dial the number of minutes between 2:25 and 2:45. This is definitely simpler than subtracting 2:25 from 2:45. Fourthly, LED displays cannot be read if the ambient light is very strong.
Electronic watches having electro-optical displays of the LC (liquid crystal) type utilize less power than watches employing LED's, however to date liquid crystal displays have not yet proven to have a satisfactorily long life. Liquid crystal displays also suffer from being inconvenient to read due to the low contrast of the display at certain viewing angles and in adverse lighting conditions. Electronic watches having LC displays have also proven to be undesirably cumbersome and bulky.
Attempts have been made to combine in an electronic watch the most favorable properties of electro-mechanical and electro-optical time displays. For example, U.S. Pat. No. 3,668,861--Mitsui, discloses an electronic watch which has electro-mechanically driven day and date displays and a pair of electro-optical hour/minute displays. The electro-optical hour/minute displays comprise discrete, parallel-functioning LC and LED displays. The parallel LC and LED displays are automatically switched by a phototransistor between the LC display during the day and the LED display when ambient lighting drops below a predetermined threshold level. The electro-optical displays present the hour and minute time functions on command only.
This prior art electronic watch thus suffers from the inconvenience of non-continuous presentation of the time functions and the high cost of providing parallel time displays for high and low ambient lighting conditions.
There is believed to be in commercial use in Japan today an electronic wristwatch having hour, minute and second hands driven by a train of pulses generated by a quartz crystal pulse generator, and in addition having an LED flashing seconds marker. This watch suffers from an unnecessarily larger power consumption and a low degree of utility and the redundancy of the information provided by the LED display.
______________________________________ Other Prior Art U.S. Patents ______________________________________ 3,712,047 Girard 3,738,099 Tanaka 3,737,746 Ceilaszyk et al 3,707,071 Walton ______________________________________
Hewlett Packard Measurement News, January/February, 1971.